Trans-Pacific temperature field in the mantle transition region derived from seismic and electromagnetic tomography

The trans-Pacific temperature field for the depth range 350-850 km was inferred from global seismic tomography and semi-global electromagnetic tomography. The seismic tomography incorporated millions of reported first arrival times and 7000 PP-P differential travel times measured on broadband seismograms. The electromagnetic tomography used voltage data from trans-Pacific submarine cables and magnetic field data from circum-Pacific geomagnetic observatories. The resultant P-wave velocity anomalies and electrical conductivity anomalies were converted to temperature anomalies using a proposed conversion formula and experimental results for mantle minerals, respectively. These conversions show consistently high-temperature anomalies of 200-300 K in the mantle transition region beneath the Hawaiian hotspot. At subduction zones, where slab-related cold anomalies and wedge mantle-related hot anomalies are likely to coexist in close proximity, the seismic and electromagnetic tomography did not always give consistent features, in part because of the preferred sensitivity of electromagnetic tomography to hot anomalies. Low-temperature anomalies of 200-300 K associated with subducted slabs are clearly resolved in the seismic tomography, but are less apparent in the electromagnetic tomography. The high-temperature anomaly in the intervening zone between the Mariana and Philippine slabs is very pronounced in the electromagnetic tomography but is marginal in the seismic tomography. (C) 2003 Elsevier B.V. All rights reserved.